Engagement of Glucocorticoid-Induced TNF Receptor Costimulates NKT Cell Activation In Vitro and In Vivo

Abstract

Glucocorticoid-induced TNF receptor (GITR) is known to provide costimulatory signals to CD4+CD25− and CD4+CD25+ T cells during immune responses in vivo. However, the functional roles of GITR expressed on NKT cells have not been well characterized. In this study, we have explored the functions of GITR as a costimulatory factor on NKT cells. GITR was found to be constitutively expressed on NKT cells and its expression was enhanced by TCR signals. GITR engagement using DTA-1, an agonistic mAb against GITR, in the presence of TCR signals, augmented IL-2 production, the expression of activation markers, cell cycle progression, and the nuclear translocations of NF-κB p50 and p65. Furthermore, GITR engagement enhanced the production of IL-4, IL-10, IL-13, and IFN-γ by NKT cells and the expression level of phosphorylated p65 in NKT cells in the presence of TCR engagement, indicating that GITR provides costimulatory signals to NKT cells. The costimulatory effects of GITR on NKT cells were comparable to those of CD28 in terms of cytokine production. Moreover, the coinjection of DTA-1 and α-galactosylceramide into B6 mice induced more IL-4 and IFN-γ production than the coinjection of control mAbs and α-galactosylceramide. In addition, the adoptive transfer of DTA-1-pretreated NKT cells into CD1d−/− mice attenuated hypersensitivity pneumonitis more than control IgG pretreated NKT cells in these mice. These findings demonstrate that GITR engagement on NKT cells modulates immune responses in hypersensitivity pneumonitis in vivo. Taken together, our findings suggest that GITR engagement costimulates NKT cells and contributes to the regulation of immune-associated disease processes in vivo.

ICOS‐dependent stimulation of NKT cells by marginal zone B cells

“…Therefore, we tested two co-stimulatory molecules -GITR and ICOSL -that can potentially shape NKT-cell responses. GITR had been shown previously to be essential for activation of NKT cells [18], while ICOSL can stimulate CD41 T cells to secrete IL-4 rather than 31].When a blocking anti-GITR antibody was added to the co-cultures of NKT cells with either MZ B cells or cDCs sensitized by aGalCer, NKT-cell proliferation and IL-4 production were not inhibited ( Fig. 6A and C).…”

“…Some studies showed that engagement of GITR leads to co-stimulation of NKT cells and increases production of IFN-g and IL-4 [18]. In contrast, others demonstrated that GITR engagement elicits co-inhibitory activity for antigen-induced NKT cells [20].…”

“…Therefore, we tested two co-stimulatory molecules -GITR and ICOSL -that can potentially shape NKT-cell responses. GITR had been shown previously to be essential for activation of NKT cells [18], while ICOSL can stimulate CD4…”

“…It has been suggested that engagement of CD40L or CD28 provides important co-stimulatory signals to NKT cells, thus modulating production of cytokines in vitro as well as in vivo [19,21,22]. Similarly, GITR was shown to provide critical signals for NKT-cell activation [18] and ICOS has been demonstrated to be required for NKT-cell survival and homeostasis in the periphery. In addition, ICOS was shown to drive the production of T H 2 cytokines [23].…”

“…However, it is more likely that particular activation situations, i.e. particular co-stimulators, promote differential NKT-cell reactions.NKT cells constitutively express receptors like CD28, CD40L, ICOS and glucocorticoid-induced TNF receptor (GITR) [8,[14][15][16][17][18][19][20]. It has been suggested that engagement of CD40L or CD28 provides important co-stimulatory signals to NKT cells, thus modulating production of cytokines in vitro as well as in vivo [19,21,22].…”